1. Field of the Invention
The present invention relates to a method and apparatus for the augmentation of convection heat transfer in a liquid which utilizes hydrodynamic forces produced by an electrical field, and more particularly to a method and apparatus for the augmentation of convection heat transfer in a liquid whereby, in a fluid transferring layer formed between a flow of liquid driven by an external source of pressure difference and a tubular member, such as in a heat exchanger tube, turbulence is produced only in the liquid in the fluid heat transferring layer formed in the vicinity of the tube's heat transfer surface, thereby suppressing the pressure loss of the flow while at the same time augmenting the heat transfer.
2. Description of the Prior Art
The degree to which convection heat transfer taking place between a heat exchange tube and a liquid flowing in the heat exchange tube can be augmented depends on how large the heat flux from the heat transfer surface to the liquid (or vice versa) can be made.
Previously, convection heat transfer in the fluid heat transferring layer was augmented by creating turbulence in the thermal boundary layer by increasing the flow velocity of the liquid, increasing the Reynolds number, or by roughening the heat transfer surface and providing obstacles to the flow of the liquid.
However, the conventional methods of augmenting convection heat transfer by producing turbulence in the flow of the liquid have had the following drawbacks.
As the turbulence produced in accordance with the above methods of augmenting convection heat transfer increases the resistance to the flow of the liquid, there is an increase in the flow energy loss and the pressure loss which necessitates the use of a larger pump, for example, resulting in higher operating costs and increased energy consumption. When the pressure loss of the flow cannot be increased, the flow velocity has to be decreased. This produces a decrease in the heat transfer coefficient and, when the method is applied to a heat exchanger, a decrease in the heat exchange efficiency.
In Japanese Patent Publication No. 59-66342 and U.S. Pat. No. 4,818,184, the present inventors disclose a method of utilizing hydrodynamic turbulence to agitate all of the fluid by providing surface electrodes and spatial electrodes arranged in opposition in the liquid and applying a high voltage across the electrodes to generate a jet stream in the liquid. Generating a high-velocity jet stream is an effective way of agitating all of the fluid but is difficult to apply to the augmentation of convection heat transfer of the liquid driven by the pressure difference through the production of turbulence only in liquid in the heat transferring layer in the vicinity of the heat transfer surface, such as when the pressure loss cannot be increased to an extent that will give rise to turbulence, or in the case of a slow flow in which a high degree of pressure loss is not possible.